Increased frequencies of CD4⁺CD25⁺ and CD8⁺CD25⁺ T cells are present in PBSC grafts of SCT recipients with GVHD. Increased frequencies of CD4⁺CD25⁺ and CD8⁺CD25⁺ T cells were present in donor PBSC grafts of those recipients who experienced GVHD (•) compared with those who did not (○). Horizontal bars indicate the mean. (A) Stratification by incidence of any GVHD after SCT. (B) Stratification by incidence of acute GVHD (grades I-IV). (C) Stratification by incidence of chronic GVHD. All P values were obtained using the Mann-Whitney U test.